Petrology of Mafic and Intermediate-Composition Magmas Associated with Rhyolite Ash-flow Volcanism, Sierra Madre Occidental

这项研究探讨了镁铁质和中等成分岩浆在Tomochic火山中心(TVC)流纹岩成因中的作用，那里的地层剖面最完整，火山活动的历史在马德雷山脉西部已知的喷发中心中得到了最好的记录。TVC最近的野外和年代学研究表明，斑状双辉石安山岩和贫晶玄武岩安山岩这两种不同的岩性是为大量流纹岩灰流喷发提供岩浆系统的重要组成部分。这些岩性和流纹岩之间的成因关系是允许的，但受到现有数据的限制很差。这项研究的主要目标将是通过：(A)比较和模拟所有岩石类型之间的矿物学、同位素(Sr、ND)和地球化学变化，以及(B)混合崩塌后熔岩的岩石学研究，进一步评估这种关系，以确定深部，拉斯瓦拉斯火山口下方储集层的镁铁质部分，以与挤压的玄武岩安山岩进行比较。这些结果将制约与流纹岩以及相关的更多镁铁质岩浆的成因有关的模型，这些岩浆位于被认为是世界上最大的“流纹岩主导”的火山田。这一结果对于将火山活动类型与构造体制联系起来的模型，以及对我们理解与大体积破火山口下储集层演化相关的过程也将是重要的。

This study addresses the role of mafic and intermediate- composition magmas in the genesis of rhyolites at the Tomochic volcanic center (TVC), where the stratigraphic section is the most complete and where the history of volcanism is best documented among known eruptive centers in the Sierra Madre Occidental. Recent field and chronologic work at the TVC has indicated that two distinct lithologies, porphyritic two-pyroxene andesite and crystal-poor basaltic andesite, were important components of the magma systems that fed large-volume rhyolite ash-flow eruptions. A genetic relationship between these lithologies and the rhyolites is allowed, but is poorly constrained, by available data. The principal goal of this study will be to evaluate that relationship further, via: (a)comparison and modeling of mineralogic, isotopic (Sr, Nd), and geochemical variations among all rock types, and (b) petrologic study of hybrid post-collapse lavas, to characterize the deep, mafic parts of the reservoir beneath the Las Varas caldera, for comparison with extruded basaltic andesite. Results will constrain model pertaining to the genesis of rhyolites, and of associated, more mafic magmas, in what is considered the world's largest "rhyolite-dominated"volcanic field. Results will also be important to models linking style of volcanism with tectonic regime, and to our understanding of processes associated with the evolution of large-volume subcaldera reservoirs.